1. Field of the Invention
The present invention relates generally to sound processing, and more particularly, to directional sound processing in a cochlear implant.
2. Related Art
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. Conductive hearing loss occurs when the normal mechanical pathways which provide sound to hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss is often addressed with conventional auditory prostheses, commonly referred to as hearing aids, which amplify sound so that acoustic information may reach the cochlea.
Profound deafness, however, is caused by sensorineural hearing loss. This type of hearing loss is due to the absence or destruction of the hair cells in the cochlea which transduce acoustic signals into nerve impulses. Those suffering from sensorineural hearing loss are thus unable to derive suitable benefit from conventional hearing aids due to the damage to, or absence of, the mechanism that naturally generates nerve impulses from sound. As a result, prosthetic hearing implants such as cochlear prostheses (commonly referred to as cochlear prosthetic devices, cochlear implants, cochlear devices, and the like; simply “cochlear implants” herein) have been developed to provide persons with sensorineural hearing loss with the ability to perceive sound.
Cochlear implants typically comprise one or more external components worn by the patient (also referred to as recipient, user, wearer and the like; “recipient” herein) and internal components that are implanted in the recipient. The external and internal components cooperate with each other to provide sound sensations to the recipient.
The external component(s) traditionally comprise several integrated or physically separate elements generally including one or more acoustical transducers that sense ambient sounds, a sound processor that selects and converts certain detected sounds, particularly speech, into coded signals, a power source such as a battery, and an external transmitter antenna.
The internal components traditionally comprise several integrated or physically separate elements generally including a receiver antenna, a stimulator unit and a carrier member on which an electrode assembly is disposed for stimulating the recipient's auditory nerve. The coded signals generated by the sound processor are transmitted transcutaneously from the external transmitter antenna to the implanted receiver antenna, commonly located within a recess of the temporal bone of the recipient. In addition to coded sound signals, this communication link is often used to transmit power to the implanted stimulator unit. Conventionally, this communication link has been in the form of a radio frequency (RF) link, although other communication and power links have been proposed and implemented with varying degrees of success.
The stimulator unit processes the coded signal and generates an electrical stimulation signal to the intra-cochlea electrode array. The electrode array typically has a plurality of electrodes that apply electrical stimulation to the auditory nerve to produce a hearing sensation corresponding to the original detected sound. Because the cochlea is partitioned into regions each responsive to stimulation signals in a particular frequency range; i.e., tonotopically mapped, each electrode of the implantable electrode array delivers a stimulation current to a particular region of the cochlea. In the conversion of sound to electrical stimulation, frequencies are allocated to stimulation channels that provide stimulation current to electrodes positioned in the cochlea at or immediately adjacent to the region of the cochlear that would naturally be stimulated in normal hearing. This enables cochlear implants to bypass the hair cells in the cochlea to directly deliver electrical stimulation to auditory nerve fibers, thereby allowing the brain to perceive hearing sensations resembling natural hearing sensations.